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Old Mar 19, 2006, 7:57 PM   #1
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I love the idea of taking pictures of waterfalls, and people crossing the street during the day, and I understand that is is a neurtral density filter that you need (right???) now I have seen some different options, such as a Hoya 4 times and 8 times, Do I need both, what is the right one for me? How will I be able to see the differences?

thanks for your time

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Old Mar 20, 2006, 6:28 AM   #2
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You won't be able to see the difference until you take the picture(s) and see if the blur was adequate.

If you're shooting on a sunny day, if you can shoot at ISO 50 you'll get -roughly- 1/100 second at f/11 without a ND filter. If you can cut the light by 4 stops, that gets you down to 1/8 second, and 8 stops would get you 2 seconds. That's at f/11, so opening up to f/8 would give you 1 second, f/5.6 1/2 second, and so on with an 8-stop ND filter.

You might want to get both filters, and use the 8-stop in bright sun and the other in shade or cloudy/overcast conditions.
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Old Apr 15, 2006, 6:56 PM   #3
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I believe the Hoya ND-4 cuts the light through it by 4x (2 stops) and the ND-8 by 8x (3 stops). These are not density ratings, where each additive increase of 1.0 amounts to a cut of 10x. On this scale, a 4x filter would be 0.6 and 8x would be 0.9 and each 2x multiplication in the attenuation would increase the density by 0.3.

For your waterfall pictures, you want something with a density between about 1.5 and 2.0, corresponding to something between 32x (5 stops) and 100x (6-2/3 stops) to allow exposure times of a large fraction of a second. Combining a 4x and an 8x filter will put you at the lower end of this attenuation range and would be OK to get your toe in these photographic waters, so to speak. If you do this kind of shooting often, you might want to consider getting a filter especially for the purpose so you don't have more reflective surfaces in front of your lens than absolutely necessary.
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